All chemicals were, unless stated otherwise, provided by the supplier and used without further purification. Dry solvents were dried by conventional laboratory methods. The eluents for chromatography petroleum ether (low-boiling) and ethyl acetate were distilled prior to use.For thinlayer chromatography silica gel 60 F254 glass plates with a layer thickness of 0.25 mm on aluminium (pore size 60 Å) from the company Merck were used. Column chromatography was performed using silica gel with a particle diameter of 40 -60 µm from the company Fluka.1 H NMR spectra were measured using the Bruker Avance 300 and Bruker Avance 500 spectrometers at 300 MHz and 500 MHz, respectively and 13 C-NMR spectra at 75 MHz and 126 MHz, respectively. Deuterated chloroform (CDCl3) and deuterated dimethyl sulfoxide (DMSO-d6) were used as solvents. The chemical shift δ in ppm (parts per million) refers to the standard tetramethylsilane. The numbering of atoms can be different from the IUPAC nomenclature in order to ensure better comparison of various compounds. In order to assign the signals of the 1 H and 13 C NMR spectra, COSY, HSQC and HMBC measurements were carried out.
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